Lithium aluminosilicate-based materials with negative thermal expansion coefficient in a broad temperature range, preparation process and use

ABSTRACT

New process for obtaining lithium aluminosilicate-based (LAS) ceramic materials having a near-zero and negative thermal expansion coefficient within a temperature range of (−150° C. to 450° C.). These materials are applicable to the manufacture of components that require a high level of dimensional stability.

FIELD OF THE ART

The present invention relates to ceramics having a negative and/ornear-zero thermal expansion coefficient, which can be used in themanufacture of components that require a high level of dimensionalstability. Therefore, the technology described in the invention fallswithin the new materials sector, while its application falls within themicroelectronics, precision optics and aeronautical sectors.

STATE OF THE ART

Materials with a low thermal expansion coefficient are those wherein thevolume variations associated to temperature changes are very small.Temperature-driven changes in the volume of materials is normallyevaluated using the thermal expansion coefficient (TEC), which isdefined as the variation in volume of a material with increasingtemperature and must always refer to the temperature range wherein saidvariation was observed.

In ceramic materials, composed of a multitude of randomly orientedcrystals, volume variation is usually extrapolated to linear variation.This is referred to as changes in elongation driven by temperaturechanges. These changes in elongation with regard to initial lengthdriven by an increase in temperature are defined as linear thermalexpansion coefficient. In general and herein, reference is made to thethermal expansion coefficient or TEC, referring to the aforementionedlinear variation. When elongation value with increasing temperature ispositive, we refer to positive TEC materials, while if this variation isnegative we refer to negative TEC materials. Materials with a low TECare materials wherein this variation in elongation is very close tozero. These materials therefore have a high level of dimensionalstability upon temperature change, due to which they are of greatinterest for a wide range of applications in very diverse fields. Thesetypes of materials are, for example, required in many types ofhigh-precision devices and instrumentation equipment in high technologysystems, and in the microelectronics and precision optics industry. Inall those applications wherein the dimensional stability of a precisionelement upon temperature change must be ensured, it will be necessary tolower the TEC of the constituent materials of those elements. Theproblem of the alteration in thermal expansion in elements manufacturedusing different materials can also be solved by means of the design ofcomposites with a required (and homogeneous) TEC. The design of thesematerials with a “customised” TEC can be addressed using a combinationof components with positive and negative expansion. This customised TECdesign of the composites can be carried out for different temperatures,in such a manner that the final field of application of componentshaving zero TEC will depend on whether they also achieve the rest of thespecific functionality characteristics required by this application. Thelithium aluminosilicate (LAS) family of ceramics and vitroceramics isfrequently used for this purpose in many fields of application, fromvitroceramics for kitchens to mirrors for satellites. Some mineralphases of this family have a negative TEC, which allows their use incomposites with a controlled and customised TEC. Materials with anegative TEC often have low fracture resistance, as their negativity isdue to a strong anisotropy between the different crystallographicorientations, wherein one of these usually exhibits negative behaviourand the other two positive behaviour. This anisotropy usually causesmicro-fissures, resulting in low values in the mechanical properties ofthese materials. In any case, the use of these expansion properties formanufacturing composites with zero TEC has a broad range of potentialapplications in engineering, photonics and electronics and in otherspecific structural applications [R. Roy et al., Annual Review ofMaterials Science, 19, 59-81 (1989)].

The LAS phase with negative expansion coefficient is β-eucryptite(LiAlSiO₄), while spodumene (LiAlSi₂O₆) has practically zero expansion.

The traditional LAS ceramic manufacturing method is based on theformation of glasses to produce vitroceramics. This method comprises themanufacture of molten material which is subsequently shaped andsubjected to thermal treatment for partial crystallisation thereof [H,Bach, Low Thermal Expansion Glass Ceramics, Springer-Verlag, Berlin,1995].

The ceramic products thus obtained are frequently heterogeneous. Onother occasions, ceramic materials are required in the absence of orwith a very low proportion of the vitreous phase, which reduces therigidity and resistance of the ceramic products. Therefore, a method formanufacturing solid-state LAS ceramics is required which, in addition tobeing inexpensive, is easy to accurately adapt the final composition ofthe material and consequently its TEC.

Sol-gel processing methods have been applied in the manufacture of LASceramics [W. Nan-Chung, Y. Sheng, U.S. Pat. No. 5,320,792 dated Jun. 14,2004] due to its multiple advantages and low processing temperatures.However, these methods are tedious, expensive and difficult to apply inindustrial processes that require large amounts of material.

Other methods for obtaining solid-state LAS ceramics use lithiumcarbonate, aluminium oxide and silicon oxide as raw materials [C.Jyh-Chen, S. Gwo-Jiun, US2004112503 dated Jun. 17, 2004]. In this paper,reference is made to calcination for obtaining a precursor and to athermal treatment applied subsequent to sintering. These authorshighlight the difficulty of sintering these ceramics.

[S. L. Swartz, U.S. Pat. No. 6,066,585 dated May 23, 2000] also makesreference to calcination for obtaining a precursor, although in thiscase they use an excess of lithium oxide, in comparison to thestechiometric composition of β-eucryptite (LiAlSiO₄), aimed at loweringsintering temperatures and increasing mechanical resistance. Thisprocedure causes the formation of second phases and consequentlymodifies the TEC values compared to monolithic β-eucryptite ceramics. Inorder to obtain better micro-structures and higher quality in LASceramics with controlled TEC values, a method including theaforementioned advantages of the sol-gel method and having industrialscalding process capacity must be developed.

The method developed herein differs from other previously publishedmethods [G. Maslennikova, Inorganic materials, 20, 9, 1984] and [A.Yamuna, et al., Journal of the American Ceramic Society, 84, 8, 2001]wherein β-eucryptite synthesis is based on the use of lithium carbonateraw materials and kaolin, as well as silica and alumina precursors suchas silica sand and commercial alumina, wherein, in addition to themodification of the structure of kaolin by addition to lithiumcarbonate, the necessary silica and alumina for adjusting thestechiometry of the β-eucryptite being formed, is added in the form of aprecursor solution, which leads to the formation of the β-eucryptitesynthesis phase at much lower temperatures, with better control over theresulting phases. In this manner, an effect similar to that achieved bymeans of sol-gel methods is achieved, with the advantage over saidsol-gel methods of being a simple, inexpensive and totally scalableprocess at industrial level.

DESCRIPTION OF THE INVENTION

The present invention is based on a new process for obtaining lithiumaluminosilicate-based (LAS) ceramic materials having a near-zero andnegative thermal expansion coefficient within the temperature range(−150° C. to 450° C.) which comprises a preparation stage of the lithiumaluminosilicate (LAS) as of kaolin, Li2CO3 and a SiO2 or Al2O3 precursorsolution. Although a process for preparing these materials has beenpublished wherein kaolin and LiCO3 are used in a powder mixture forpreparing the LAS precursor [O. V. Kichkailo and I. A. Levitskii, Glassand Ceramics, 62, 5-6, 2005] and [A. Yamuna, et al., Journal of theAmerican Ceramic Society, 84, 8, 2001], a process that uses a SiO2 orAl2O3 precursor solution in this stage of the preparation had never beenpublished. The use of this SiO2 or Al2O3 precursor solution represents anovel aspect and a significant technical advantage with respect to othermethods mentioned in the literature, as it is essential for obtainingβ-eucryptite at a low temperature with control of the pure phases and,consequently, with a more accurately adjusted TEC.

Therefore, one aspect of the present invention is the process forpreparing lithium aluminosilicate-based ceramic materials having anear-zero and negative thermal expansion coefficient within thetemperature range 31 150° C. to 450° C., which comprises a stage forpreparing the lithium aluminosilicate precursor as of kaolin, Li2CO3 anda SiO2 or Al2O3 precursor solution.

A preferred aspect of the present invention is the process for obtainingceramic materials, hereinafter referred to as the process for preparingceramic materials of the invention, characterised in that it comprisesthe following stages:

a. synthesis of the lithium aluminosilicate precursor by means of thepreparation of a kaolin suspension, Li2CO3 and a SiO2 or Al2O3 precursorsolution,

b. calcination of the resulting powder after drying the mixture obtainedin a),

c. milling and drying of the material obtained in b),

d. shaping of the material obtained in c),

e. sintering of the material obtained in d).

A more preferred aspect of the present invention is the process forpreparing ceramic materials of the invention wherein tetraethylorthosilicate is used as a SiO2 precursor.

Another more preferred aspect of the present invention is the processfor preparing ceramic materials of the invention wherein aluminiumethoxide as an alumina precursor.

Another more preferred aspect of the present invention is the processfor preparing ceramic materials of the invention wherein the suspensionof stage a) is an alcohol.

Another more preferred aspect of the present invention is the processfor preparing ceramic materials of the invention wherein the calcinationof stage b) is carried out at a temperature comprised between 400° C.and 970° C. for a period comprised between 1 and 240 hours.

Calcinations at a temperature of 900° C. transform the structure ofkaolin, directly giving a β-eucryptite-type structure. Lowertemperatures can be used, but using longer calcination times. Thetransformation of the structure of α into β in the eurocryptite normallytakes place at 970° C., due to which the calcination temperature must begreater than or equal to 970° C. in order to obtain a LAS precursorhaving a single β-eucryptite-type structural phase. In this processlower calcination temperatures have been achieved, obtaining the β phaseas a result. A particular embodiment of the present invention is theprocess for preparing ceramic materials of the invention wherein thecalcination of stage b) is carried out at a temperature of 900° C. for aperiod of 2 hours.

Another more preferred aspect of the present invention is the processfor preparing ceramic materials of the invention wherein the calcinationof stage b) is carried out after sifting the solid obtained on dryingthe suspension obtained in a).

Another more preferred aspect of the invention is the process forpreparing ceramic materials of the invention wherein the milling ofstage c) is carried out by attrition in a high-energy mill.

By means of the high-energy attrition mill, a β-eucryptite powder with avery fine grain size is obtained. This very fine grain size is essentialto subsequently obtaining ceramic LAS bodies having a high relativedensity with enhanced mechanical properties.

Another particular embodiment of the present invention is the processfor preparing ceramic materials of the invention wherein attrition inthe high-energy mill is carried out operating at 100-400 r.p.m.preferably 350 r.p.m., for periods of more than 20 minutes.

Another more preferred aspect of the present invention is the processfor preparing ceramic materials of the invention wherein the drying ofstage c) is carried out by means of atomisation.

Another more preferred aspect of the present invention is the processfor preparing ceramic materials of the invention wherein the shaping ofthe material of stage d) is carried out by means of isostatic pressing.

Another particular embodiment of the present invention is the processfor preparing ceramic materials of the invention wherein the shaping ofthe material of stage d) is carried out by means of cold isostaticpressing and at pressures of between 100 and 400 MPa, preferably 200MPa.

Another more preferred aspect of the present invention is the processfor preparing ceramic materials of the invention wherein the sinteringof stage e) is carried out at a temperature of between 900° C. and1,500° C.

Another particular embodiment of the present invention is the processfor preparing ceramic materials wherein the sintering of stage e) iscarried out at a temperature of 1,350° C.

A particular example of the present invention is the process forpreparing ceramic materials of the invention wherein a temperature rampof 2-10° C./min, preferably 5° C./min, is used, maintaining the finaltemperature for a period comprised between 1 and 4 hours, and asubsequent cooling of up to 900° C. using a temperature ramp of 2-10°C./min, preferably 5° C./min.

Another more preferred aspect of the present invention is the processfor preparing ceramic materials of the invention wherein stages d) ande) are carried out using the hot-press technique.

The hot-press technique is based on the simultaneous application ofpressure and high temperature to accelerate densification speed. In thistechnique, heating takes place by means of graphite resistors.

Another particular embodiment of the present invention is the processfor preparing ceramic materials of the invention wherein stages d) ande) are carried out using the hot-press technique at a temperaturecomprised within the range of 900-1,400° C., preferably 1,100° C.

Another particular embodiment of the present invention is the processfor preparing ceramic materials of the invention wherein stages d) ande) are carried out using the hot-press technique at a pressure of 5 and80 MPa, preferably 15 MPa.

Another more preferred aspect of the present invention is the processfor preparing ceramic materials of the invention wherein stages d) ande) are carried out using the spark plasma sintering (SPS) technique.

The spark plasma sintering technique is also based on the simultaneousapplication of pressure and high temperature. As opposed tohot-pressing, this technique is based on the application of sparkdischarges through the graphite moulds and the sample, allowing the useof heating speeds in the order of hundreds of degrees per minute.

Another particular embodiment of the present invention is the processfor preparing ceramic materials of the invention wherein stages d) ande) are carried out using the spark plasma sintering (SPS) technique at atemperature comprised between 900° C. and 1,400° C., preferably 1,100°C.

Another particular embodiment of the present invention is the processfor preparing ceramic materials of the invention wherein stages d) ande) are carried out using the spark plasma sintering (SPS) technique, fora period of more than 1 minute, preferably 5 minutes.

Another particular embodiment of the present invention is the processfor preparing ceramic materials of the invention wherein stages d) ande) are carried out using the spark plasma sintering (SPS) technique at apressure comprised between 5 and 80 MPa, preferably 50 MPa.

Another aspect of the present invention is the ceramic material preparedusing any of the previously described processes.

The ceramic materials of the present invention have negative and/ornear-zero TEC values for a broad temperature range (between −150° C. and450° C.). The mechanical properties of the materials prepared by meansof this invention are better than those of materials with negative TECvalues available to date, which have values of approximately 35 MPa andE values of approximately 36 GPa [S. L. Swartz, U.S. Pat. No. 6,066,585dated May 23, 2000].

Another preferred aspect of the present invention is the lithiumaluminosilicate-based ceramic material prepared using the process forpreparing ceramic materials of the invention, wherein its final densityis 98% higher than the theroretical density and its thermal expansioncoefficient is <0.5×10⁻⁶ K⁻¹ within the temperature range −150° C. to450° C.

The composition of the LAS ceramic materials of the present inventionlies between spodumene and eucryptite, i.e. Li₂O:Al₂O₃:SiO₂ between1:1:4 and 1:1:2. The main phase in the sintered material is aβ-eucryptite solid solution which is stable at relatively hightemperatures.

Another aspect of the present invention is the use of ceramic material,prepared using any of the previously described processes, in themanufacture of new materials.

Another preferred aspect of the present invention is the use of theceramic material, prepared by means of any of the previously describedprocesses, in the manufacture of components that require a high level ofdimensional stability, such as for example high-precision measuringinstruments, mirrors for space observation systems, whether terrestrialor aerial, optical lithography scanners, holography, laser instrumentsor heat dissipaters.

DESCRIPTION OF THE FIGURES

FIG. 1 shows X-ray diffractogrammes corresponding to the LAS materialsobtained in examples 1, 2 and 3. The β-eucryptite solid solution isindicated by the peaks circled in white. The peaks corresponding tolithium aluminosilicate (examples 1 and 3) are indicated by blacktriangles.

FIG. 2 shows photographs of the materials obtained in example 2 obtainedusing a scanning electron microscope, wherein the formation of a smallpercentage of vitreous phase (lighter grey) and scarce porosity can beobserved.

FIG. 3 shows dilatometries corresponding to the materials prepared inthe different examples: example 1: dashed line; example 2: continuousline: example 3: dotted line.

EXAMPLES OF EMBODIMENT

A series of trials conducted by the inventors, which are representativeof the effectiveness of the process of the invention for obtaining a LASmaterial having a negative or near-zero thermal expansion coefficient inthe temperature range of −150° C. to 450° C., are described below. Theseexamples are shown in FIGS. 1 to 3.

The method comprises the synthesis of a ceramic powder by means ofcalcination treatments prior to a high-energy milling stage essential toobtaining an improved microstructure of the final dense ceramicmaterial.

Example 1 Synthesis of a LAS Precursor Having Greater SiO2 Content ThanThat of the Starting Kaolin and Subsequent Densification Thereof byMeans of Sintering in a Conventional Oven

The synthesis of ceramic powder starts by preparing the startingmaterials. This implies the use of kaolin, in this example “Arcano”kaolin from Moltuval (Spain), with a composition ofAl₂O₃.2.37SiO₂.2.67H₂O; lithium carbonate RECTAPUR (99%, VWR Prolabo)and tetraethyl orthosilicate (TEOS) (99.5%, Sigma-Aldrich). Theappropriate quantities of kaolin (528.7 g) are dispersed in 2 litres ofethanol. This dispersion is mechanically agitated at ambienttemperature. The appropriate quantity of lithium carbonate (131.9 g) isthen added to the dispersion, continuing agitation. Finally, the TEOS(339.4 g) is slowly added while gradually continuing agitation thereof.After mixing the raw materials, agitation is continued for 1 hour. Thesuspension thus obtained is dried by evaporation of the solvent, raisingthe temperature to 80° C. while continuing agitation. When practicallyall of the solvent has evaporated, the nearly dry suspension isintroduced in an oven at 120° C. in order to complete drying thereof.

The dry mixture is sifted prior to the calcination treatment in order toreach graining below 63 μm using a 63 μm sieve.

Next, the calcination process is carried out for the formation of theLAS precursor, to which end the powder is placed in alumina crucibleswhich are introduced in an oven. The calcination treatment was carriedout at 900° C. for 2 hours with a temperature ramp of 5° C./min.

After calcination, the starting powder is transformed into the LASprecursor. This precursor is a β-eucryptite solid solution, thecomposition of which is verified by means of X-ray diffraction.

The next step consists of attrition of the precursor in a high-energymill. To this end, a stable precursor suspension is prepared andintroduced in the mill, dispersing the precursor powder in ethanol (40%of solid content) by mechanical agitation for 60 minutes. The attritionmill, with a 9/1 content of alumina balls, operated at 350 r.p.m. for 60minutes, The precursor has a sub-micrometric size after milling. Thesuspension thus obtained is dried by atomisation at the same time thatthe solvent is recovered.

The dry precursor is shaped by means of cold isostatic pressing at 200MPa.

This shaped material is sintered in an oven at 1,350° C. for 2 hourswith a temperature ramp of 5° C./min. Cooling is controlled up to 900°C. at the same speed.

Characterisation has been carried out by means of X-ray diffraction forthe purpose of controlling the resulting association of phases in thesintered material. The diffractogramme corresponding to the materialobtained according to this example of embodiment is shown in FIG. 1. Inthis example, the ceramic body consists mainly of a β-eucryptite solidsolution. Small traces of LiAlO2 have been detected. Small traces ofvitreous phase (<2vol %) have also been detected in the images ofretro-dispersed electrons obtained by scanning electron microscopy, adetailed view of which is shown in FIG. 2. This small percentage ofglass aids sintering without affecting the mechanical properties.

The sintered sample has been characterised using a Netszch DIL402Cdilatometer to obtain the TEC value. The corresponding curve is shown inFIG. 3. The Young module was determined by means of the resonancefrequency method, using a Grindosonic apparatus. Its fracture resistancewas determined by conducting a four-point bend test using INSTRON 8562testing equipment. The results of these properties are shown in Table I.

Example 2 Synthesis of a LAS Precursor Having a Higher Al2O3 ContentThan That of the Starting Kaolin and Subsequent Densification Thereof byMeans of Spark Plasma Sintering

The synthesis of ceramic powder starts by preparing the startingmaterials. This implies the use of kaolin, in this example “Arcano”kaolin from Moltuval (Spain), with a composition ofAl₂O₃.2.37SiO₂.2.67H₂O; lithium carbonate RECTAPUR (99%, VWR Prolabo)and aluminium ethoxide (>97%, Sigma-Aldrich). The appropriate quantitiesof kaolin (550.3 g) are dispersed in 2 litres of ethanol. Thisdispersion is mechanically agitated at ambient temperature. Theappropriate quantity of lithium carbonate (164.7 g) is then added to thedispersion, continuing agitation thereof. Finally, the aluminiumethoxide (111.3 g) is slowly added while gradually continuing agitation.After mixing the raw materials, agitation is continued for 1 hour. Thesuspension thus obtained is dried by evaporation of the solvent, raisingthe temperature to 80° C. while continuing agitation. When practicallyall of the solvent has evaporated, the nearly dry suspension isintroduced in an oven at 120° C. in order to complete drying thereof.

The dry mixture is sifted prior to the calcination treatment in order toreach graining below 63 μm using a 63 μm sieve.

Next, the calcination process is carried out for the formation of theLAS precursor. The powder is placed in alumina crucibles which areintroduced in an oven. The calcination treatment was carried out at 900°C. for 2 hours with a temperature ramp of 5° C./min.

After calcination, the starting powder is transformed into the LASprecursor. This precursor is a β-eucryptite solid solution, thecomposition of which is verified by means of X-ray diffraction.

The next step consists of attrition of the precursor in a high-energymill. To this end, a stable precursor suspension was prepared andintroduced in the mill, dispersing the precursor powder in ethanol (40%of solid content) by mechanical agitation for 60 minutes. The attritionmill, with a 9/1 content of alumina balls, operated at 350 r.p.m. for 60minutes. The precursor has a sub-micrometric size after milling. Thesuspension thus obtained is dried by atomisation at the same time thatthe solvent is recovered.

The dry precursor is introduced in a graphite mould and subjected to aninitial uniaxial pressure of 5 MPa. Next, the material is sintered usingthe SPS technique with the following experimental variables: heatingspeed of 25° C./min, maximum temperature of 1,150° C., maximum pressureof 50 MPa, permanence time of 5 minutes at maximum temperature andpressure.

Characterisation has been carried out by means of X-ray diffraction forthe purpose of controlling the resulting association of phases in thesintered material. The diffractograrnme corresponding to the materialobtained according to this example of embodiment is shown in FIG. 1. Inthis example, the ceramic body consists mainly of a β-eueryptite solidsolution. As in the preceding example, small traces of the vitreousphase were also detected.

The sintered sample has been characterised using a Netszch DIL402Cdilatometer to obtain the TEC value. The corresponding curve is shown inFIG. 3. The Young module was determined by means of the resonancefrequency method, using a Grindosonic apparatus. Its fracture resistancewas determined by conducting a four-point bend test using INSTRON 8562testing equipment. The results of these properties are shown in Table I.

Example 3 Synthesis of a LAS Precursor Having a Higher SiO2 Content ThanThat of the Starting Kaolin and Subsequent Densification Thereof byMeans of Hot-Pressing

The synthesis of ceramic powder starts by preparing the startingmaterials. This implies the use of kaolin, in this example “Arcano”kaolin from Moltuval (Spain), with a composition ofAl₂O₃.2.37SiO₂.2.67H₂O; lithium carbonate RECTAPUR (99%. VWR Prolabo)and tetraethyl orthosilicate (99.5%, Sigma-Aldrich). The appropriatequantities of kaolin (528.7 g) are dispersed in 2 litres of ethanol.This dispersion is mechanically agitated at ambient temperature. Theappropriate quantity of lithium carbonate (131.9 g) is then added to thedispersion, continuing agitation. Finally, the TEOS (339.4 g) is slowlyadded while gradually continuing agitation thereof. After mixing the rawmaterials, agitation is continued for 1 hour. The suspension thusobtained is dried by evaporation of the solvent, raising the temperatureto 80° C. while continuing agitation. When practically all of thesolvent has evaporated, the nearly dry suspension is introduced in anoven at 120° C. in order to complete drying thereof.

The dry mixture is sifted prior to the calcination treatment to reachgraining below 63 μm using a 63 μm sieve.

Next, the calcination process is carried out for the formation of theLAS precursor. The powder is placed in alumina crucibles which areintroduced in an oven. The calcination treatment was carried out at 900°C. for 2 hours with a temperature ramp of 5° C./min.

After calcination, the starting powder is transformed into the LASprecursor. This precursor is a β-eucryptite solid solution, thecomposition of which is verified by means of X-ray diffraction.

The next step consists of attrition of the precursor in a high-energymill. A stable precursor suspension was prepared and introduced in themill, dispersing the precursor powder in ethanol (40% of solid content)by mechanical agitation for 60 minutes. The attrition mill, with a 9/1content of alumina balls, operated at 350 r.p.m. for 60 minutes. Theprecursor has a sub-micrometric size after milling, The suspension thusobtained is dried by atomisation at the same time that the solvent isrecovered.

The dry precursor is introduced in a graphite mould and subjected to aninitial uniaxial pressure of 5 MPa. Next, the material is sintered bymeans of hot-pressing with the following experimental variables: heatingspeed of 5° C./min, maximum temperature of 1,150° C., maximum pressureof 15 MPa, permanence time of 1 hour at maximum temperature andpressure.

Characterisation has been carried out by means of X-ray diffraction forthe purpose of controlling the resulting association of phases in thesintered material. The diffractogramme corresponding to the materialobtained according to this example of embodiment is shown in FIG. 1. Inthis example, the ceramic body consists mainly of a β-eucryptite solidsolution. As in the preceding examples, small traces of LiAlO2 andvitreous phase were also detected.

The sintered sample has been characterised using a Netszch DIL402Cdilatometer to obtain the TEC value. The corresponding curve is shown inFIG. 3. The Young module was determined using the resonance frequencymethod, using a Grindosonic apparatus. Its fracture resistance wasdetermined by conducting a four-point bend test using INSTRON 8562testing equipment. The results of these properties are shown in Table I.

TABLE I Property Example 1 Example 2 Example 3 Density % 95.6 99.3 98.5Yound Mod. (GPa) 35 107 96 Resistance (MPa) 37 110 99 TEC between −150°C. and 450° C. −1.13 0.45 −0.33 (1/K * 10−6)

1-23. (canceled)
 24. A lithium aluminosilicates based ceramic materialprepared by a process comprising the steps of: a) preparing a lithiumaluminasilicate precursor comprising kaolin suspension, Li₂CO₃ and aprecursor solution of SiO₂ or Al₂O₃ and drying said aluminosilicateprecursor to form a powder, b) calcining the powder obtained in step a),c) milling and drying the powder obtained in step b), d) shaping thepowder obtained in step c) to form a shaped material, and e) sinteringthe shaped material obtained in step d).
 25. The lithiumaluminosilicate-based ceramic material, according to claim 24, whereinits final density is greater than 95% of theoretical density and itsthermal expansion coefficient is <0.5×10-6 K-1 within the temperatureinterval of −150° C. to 450° C. 26-27. (canceled)
 28. A lithiumaluminosilicate-based ceramic material with thermal expansioncoefficient of <0.5×10-6 K-1 within the temperature interval of −150° C.to 450° C. and a single beta-crystalline phase characterized by X-raypowder diffraction pattern having at least 19.4±0.3, 34.6±0.3, 38.1±0.3,39.5±0.3, 43±0.3, 47.8±0.3, 56.0±0.3 and 63.6±0.3 peaks in degrees 2Θthat are identified as characteristic peaks of crystallinebeta-eucryptite phase.
 29. New materials comprising components thatrequire a high level of dimensional stability and the ceramic materialaccording to claim 24, selected from the group consisting ofhigh-precision measuring instruments, mirrors for space observationsystems, whether terrestrial or aerial, optical lithography scanners,holography, laser instruments and heat dissipaters.
 30. New materialscomprising components that require a high level of dimensional stabilityand the ceramic material according to claim 26, selected from the groupconsisting of high-precision measuring instruments, mirrors for spaceobservation systems, whether terrestrial or aerial, optical lithographyscanners, holography, laser instruments and heat dissipaters.